Carbon materials are applied for low temperature fuel cells, electrodes of respective supercapacitors or catalyst carriers in liquid-phase catalytic reaction. Therefore, the carbon material becomes important more than ever while the cost reduction for the production of the carbon materials is more and more required. In the use of the carbon materials as the electrodes or the catalyst carriers, the high porosities of the respective carbon materials are important in view of high fluidity of gas and liquid. In the use of the carbon materials as the electrodes, the high electric conductivities and current densities of the respective carbon materials are important. As a carbon material satisfying the above-described requirements can be exemplified a carbon sintered body commercially available wherein platinum particles are dispersed in carbon nanotubes or carbon nanohorns and sintered at high temperature or carbon fibers are mixed with a carbon material and sintered.
The thus obtained carbon material is, however, shaped in a form of sheet by firing the carbon nanotubes, the carbon nanohorns or the carbon fibers, which are inherently separated, at high temperature. In this case, the high porosity and the high electric conductivity in a medium transmission direction of the carbon material are conflicting factors one another.
The porous carbon material, on the other hand, raises expectations for a hydrogen storage capacitor functioning as a metallic atom/cluster supporting carbon nano-sized micropore material by itself. As a carbon material capable of exhibiting the above-described effect/function, an attention is paid to such a carbon nanotube. However, the storage performance of the carbon nanotube cannot be practically utilized under low pressure. Alternatively, a metallic material has some problems of heavy weight thereof and being incapable of exhausting hydrogen stored therein if the metallic material is not positioned at high temperature practically impossible, resulting in not being practically utilized.
In Patent reference 1, in this point of view, a porous structural material is made by using a carbide and a halogen. Such a technique, however, teaches only to control the combination of the carbide and the halogen to be employed to control the sizes of pores of the material, but does not refer to the increase and decrease of the pores at all. The carbon structural material, therefore, does not satisfy the high porosity and high electric conduction sufficiently.
Recently, the cost of gasoline is raised so that the energy problems become critical issue. For example, a hybrid system or the like is being developed in order to convert the kinetic energy generated by the combustion of gasoline in an automobile engine into the corresponding electric energy in view of the effective utilization of the gasoline. Such a hybrid system requires an electric storage device capable of conducting electric charge and discharge under the condition of large current and high speed. As the electric storage device may be exemplified a nickel hydride/lithium secondary battery, a supercapacitor or a combination thereof.
The supercapacitor is called as an electric double layer capacitor and electrically charged by adsorbing minus ions on the surface of the positive electrode thereof and plus ions on the surface of the negative electrode thereof. In order to enhance the capacitance of the supercapacitor sufficiently, the surface areas of the positive and negative electrodes thereof are increased as large as possible so that the ions are adsorbed onto the positive and negative electrodes thereof as much as possible.
In this point of view, as the electrode material of the supercapacitor would be used a porous carbon material because the porous carbon material has an electric conduction to some degrees and does not generate the chemical reaction for the electrolyte material. For example, the porous material is made by contacting a given carbon material with a moisture at high temperature for the formation of pore or by alkali activation of treating a given carbon material with a molten salt of alkaline metal hydroxide.
In the case that the carbon material is rendered porous with the moisture, there are problems that the electrostatic capacitance per unit volume of the carbon material is decreased even though the substantial surface area of the carbon material is increased because the bulk density of the carbon material is decreased and the production yield for the porous carbon material is decreased. In the alkaline activation, there is a problem that the volume expansions of the thus obtained electrodes at initial electric charge become large, which may result in the breakage of the cell of the supercapacitor in an extreme case. There is also a problem that the device cost of the supercapacitor becomes too large for ensuring its safety because the resultant alkaline metal as a byproduct is higher reactive.
In both techniques, therefore, a supercapacitor usable practically and the porous carbon material usable for the supercapacitor cannot be provided.
In this point of view, such an attempt as obtaining a porous carbon material with a sufficient specific surface area is made from the beginning without the use of the post-treatment such as the moisture exposure and the alkaline molten salt treatment. For example, Patent reference 2 teaches that an organic resin such as a polyvinyl alcohol or a polystyrene is heated with inorganic particles made of, e.g., magnesium oxide to precipitate the resultant carbides on the surfaces of the inorganic particles and then remove the resultant carbides by means of acid cleaning, thereby producing a porous carbon material.
However, there is a problem that the porous carbon material obtained by the above-described method is not excellent in production yield so that the cost of the porous carbon material is raised. There is also a problem that the specific surface area of the porous carbon material cannot be realized so that the porous carbon material cannot have an electrostatic capacitance enough to be used as a supercapacitor.
Patent Reference 1: US 2006/0165584 A1
Patent Reference 2: JP-A 2006-062954 (KOKAI)